There are many objects, such as a picture frame, a window frame etc., which are constructed with a generally square frame structure. One of the conventional methods of manufacturing such square frames is, for example, to produce four pieces of frame woods, each of which is cut at 45.degree. at both ends in, order to form a square frame successively, and then to miter these frame sides with iron nails or adhesive so as to form a square frame by forming miter joints. However, the drying of the adhesive takes additional time such that if the square frame is inadvertently tampered with during the drying of the adhesive, it usually causes crookedness or inadequate positioning of the square frame. Moreover, when coupling of these frame joints is accomplished by means of iron nails, errors cause waste of time and it is difficult to connect these frame sides to the adequate positions respectively.
Accordingly, in view of these disadvantages and inconveniences described above, the inventor of the present invention, after research and experiment, has invented a fixing tool for a square frame.